The present invention relates to coding of a sequence of symbols into a different sequence of symbols in a manner that modifies the statistical properties of the original sequence. More specifically it relates to coding a message of m-valued symbols into a message of n-valued symbols with n>m.
For illustrative purposes messages using symbols that may represent text are used herein. It is to be understood that any message, including but not limited to a text message, a data message, an audio message, a video message or any message that applies symbols may apply the coding and/or decoding methods and systems disclosed herein as an aspect of the present invention.
It is known that text messages based on letters or other symbols comprise important statistical information related to the applied language. For instance frequency analysis of letters in an English text message of sufficient length will show that the letters ‘e’ and ‘t’ occur the most often. Such analysis can also be applied to combinations of 2 letters (digrams), such as ‘th’ and ‘ea’ or combinations of even more letters. Such a frequency analysis will provide important information about an encrypted message and may form the basis for cryptanalysis.
Known statistical technologies can provide a cryptanalyst important hooks to start deciphering an enciphered message. Current encryption methods may apply keys. A key may be a known series of symbols against which a message may be coded or decoded. Cryptanalysis of the ciphers is known to be difficult and very resource intensive. However ultimately statistical assumptions, combined with brute force calculations have proven to help break many codes. Clearly it would be helpful the security of a message if one could modify the statistical distribution of symbols of a message, whereby the modification will not affect the content or cleartext of a message and the coding and decoding can be performed automatically with a computer program.
Performance of transmission systems, may improve if the energy in a message is distributed equally and uniformly over time and over individual channels.
Accordingly novel and improved methods and systems are required that can modify statistical information of a message to resist cryptanalysis or to obtain better transmission performance.